1. Field of the Invention
The present invention relates to a fiber ring laser, and more particularly, to a fiber ring laser capable of emitting a laser beam with multiple wavelengths.
2. Description of Related Art
Fiber communication technology provides an extremely wide bandwidth, which facilitates the users to enjoy rapid and convenient network service. However, the fiber communication components are quite expensive due to the complex processes or the materials, so the communication technology is mainly used in the backbone network. Currently, the methods of division multiplexing in the fiber communication technology include time division multiplexing, wavelength division multiplexing, code division multiplexing, etc. For the purpose of achieving the full duplex in the fiber communications technology, the upstream signals and downstream signals are mostly required to have two different wavelengths.
Accordingly, in order to generate a laser beam with a plurality of different wavelengths, many research institutions and manufacturers of fiber communication components have developed a variety of lasers capable of emitting a laser beam with different wavelengths, for the application in optical metro network, optical access network, and optical fiber sensor system.
Referring to U.S. Pat. No. 6,560,247, Chang et al. set forth a laser capable of emitting a dual-wavelength laser beam. However, the dual-wavelength laser needs several short periodic Fiber Bragg Gratings (FBGs) to form two resonant cavities with specified wavelengths and attain a laser beam with two specified wavelengths. The precise FBG requires a fine coating technique, thus raising the cost of the dual-wavelength laser.
Referring to U.S. Pat. No. 6,407,855, MacCormack et al. set forth a laser capable of emitting a multi-wavelength laser beam at a time. The multi-wavelength laser uses cascaded Raman resonators and a plurality of precise FBGs for emitting the multi-wavelength laser beam. However, the multi-wavelength laser needs a Raman resonator, which aggregates the nonlinear effect of the overall laser. Therefore, an expensive high-power pumping laser must be added. The multi-wavelength laser needs a precise FBG and expensive high-power pumping laser, thus leading to a high manufacturing cost of the multi-wavelength laser.
Further, referring to Bamdad Bakhshi, and Peter A. Andrekson, “Dual-Wavelength 10-GHz Actively Mode-Locked Erbium Laser”, IEEE Photonics Technol. Lett., November, 1999, vol. 11, p.p. 1387-1389”, Bakhshi et al. set forth a dual-wavelength laser that needs two Raman pumping lasers and requires a complex mode-locking circuit, so the cost is till high.
Finally, referring to “Xueming Liu, “A Dual-Wavelength Sampled Fiber Bragg Grating and its Application in L-band Dual-wavelength Erbium-Doped Fiber Lasers”, IEEE PHOTONICS TECHNOLOGY LETTERS, 18 (17-20): 2114-2116 SEPTEMBER-OCTOBER 2006”, Xueming Liu set forth a dual-wavelength laser that needs the FBG as well and adopts the Raman pump. Therefore, the dual-wavelength laser provided by Xueming Liu still has the problem of the cost.
In view of above, the conventional multi-wavelength or dual-wavelength laser needs a passive optical filter (for example, FBG) in the fiber ring, and requires a Raman pumping laser to emit the dual-wavelength and multi-wavelength laser. Therefore, the cost of the conventional multi-wavelength or dual-wavelength laser is high.